Joint arthroplasty is a well known surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. Joint arthroplasty is commonly performed for hips, knees, elbows, and other joints. The health and condition of the joint to be replaced dictate the type(s) of prosthesis necessary to replace the natural joint. The hip joint includes the acetabulum of the pelvis which receives the head or ball of a femoral component. Replacement of the acetabulum is necessary when there is an inadequate articulation surface for a head or ball of a femoral component, natural or prosthetic. Prosthetic components that are used in a hip arthroplasty include acetabular cups and acetabular liners. An acetabular cup is implanted in the acetabular cavity in the pelvis to replace the natural acetabulum and the liner provides the bearing surface.
FIG. 1 shows an exemplary acetabular replacement system 10 including an acetabular cup 12, an acetabular liner 14 and a constraining ring 16. The acetabular cup 12 includes a cavity 18 which is configured to receive the acetabular liner 14. The acetabular liner 14 includes an outer surface 20 configured to be received by the cavity 18 and a lip 22 defining an opening to a cavity 24.
The acetabular system 10 may be used with a femoral system 26 shown in FIG. 2. The femoral system 26 includes a stem 28, a neck 30 and a femoral ball 32. The cavity 24 is configured to receive the femoral ball 32. The cavity 24 is slightly more than a hemispherical cavity and the diameter defined by the lip 22 is less than the diameter of the femoral ball 32. Thus, once the femoral ball 32 is received into the cavity 24, the potential for inadvertent dislocation of the hip joint is reduced. In order to allow the ball 32 to be positioned within the cavity 24, the lip 22 is somewhat flexible. The constraining ring 16 is positioned over the lip 22 to restrict flexure of the lip 22 after the ball 32 is positioned within the cavity 24.
To implant an acetabular cup such as the acetabular cup 12, a cavity is reamed in the pelvis of a patient. The reamed cavity generally conforms to the outer surface of the acetabular cup 12. The acetabular cup 12 is then inserted into the formed cavity and secured to the native bone. The acetabular cup 12 is positioned in the pelvis at a fixed orientation in the acetabulum so as to emulate the patient's natural anatomy. The implanted cup 12 should remain stable to prevent erosion of the surrounding bone and to inhibit generation of excessive wear debris in the prosthetic joint.
Various methods and techniques have been used to secure an acetabular cup within a formed acetabular cavity. One such method includes the use of bone cement to secure the acetabular cup to the acetabulum. Another technique utilizes an acetabular cup having holes for receiving screws, or other types of fasteners, to affix the acetabular cup to bone. A further method includes the implantation of an acetabular cup having an outer surface with various surface features to enhance fixation of the cup within the acetabular cavity. Two or more of these methods may be used in conjunction with each other to secure the acetabular cup to the acetabulum.
No matter which technique(s) are used to secure the acetabular cup, proper initial positioning of the acetabular cup within the reamed cavity is critical to the proper functioning of the prosthetic component. The positioning of the cup is complicated by the fact that incisions used in hip or femoral operations may be quite deep, with the implantation site remote from the initial incision location. Moreover, it is desired to keep the incision as small as possible both for improved healing as well as aesthetic purposes.
Next, the liner 14 is inserted into the acetabular cup 12. The liner 14 acts as a bearing surface against which the ball or head of the femoral component presses. The implantation of a liner presents many of the same difficulties as the implantation of a cup. The instruments used to keep the incision site open crowd the incision area and obscure the surgeon's vision. Thus, the liner must be manipulated into position in a very confined space. Moreover, care must be taken to ensure that no tissue is trapped between the acetabular cup and the acetabular liner as the liner is being inserted. Obviously, obscuring the vision of the surgeon hinders the procedure and can result in undesired delays.
Once the acetabular line 14 is positioned within the acetabular cup 12, the surgeon performs a range of motion procedure to verify that the acetabular cup 12 and liner 14 are properly positioned. The range of motion procedure involves insertion of the femoral ball 32 into the cavity 24 and manipulation of the patient's leg through various positions. When the range of motion procedure is satisfactorily completed, the surgeon inserts the constraining ring 16 onto the acetabular lip 22, thereby inhibiting the ability of the lip 22 to flex. Accordingly, the femoral head 32 is constrained within the acetabular liner 14.
Manipulation of the constraining ring 16 implicates many difficulties which are similar to the difficulties in placing an acetabular cup or an acetabular liner. Additional difficulties, however, are presented due to the manner in which the constraining liner must be positioned. In order to position the constraining ring 16 on the lip 22, the constraining ring 16 must be pre-positioned on the neck 30 as shown in FIG. 3 prior to positioning the femoral ball 32 into the cavity 24. Accordingly, the constraining ring must be located within the surgical site while the femoral component 26 and the acetabular system 10 are manipulated. Thus, any device used to install the constraining ring could further encumber the manipulation of the femoral component and the acetabular component thereby delaying the procedure.
Additionally, the actual insertion of the constraining ring is difficult and awkward. Thus, the polyethylene liner may be inadvertently damaged, further delaying the procedure.
What is needed therefore is an apparatus and method for positioning a constraining ring on an acetabular liner which overcomes one or more of the above-mentioned disadvantages.